The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.
The evolvement of communication technology, particularly IP-based communication technology and end user terminals, has enabled versatile communication possibilities and introduction of different services. More and more often services are implemented using primitives provided by SIP (session initiation protocol) which is not vertically integrated into a communications system but a tool to build a multimedia architecture. More precisely, SIP is an IETF defined application-layer control (signalling) protocol for creating, modifying, and terminating sessions with one or more participants.
One special feature which may utilize SIP sessions is group communication. The term “group”, as used herein, refers to any logical group of two or more users, i.e. group members, intended to participate in the same group communication, and group communication covers a session between two or more participants. Examples of group communication include conferencing, Internet telephone calls, multimedia distribution, multimedia conferencing, instant messaging, and chatting.
Due to the versatile communication possibilities, different media types can be usable in a group, such as voice, instant messages, video, gaming service, music, file transfer, etc. Typically only some of the above media types are used in a session. A user wanting to establish a session with other group members may send a SIP request having an SDP (session description protocol) offer defining media types the user wants to offer for the session. However, a policy or a rule may have been defined which may cause that one or more of the offered media types will be rejected by a server controlling the session establishment or a group member, for example, since the session already exists. One of the problems associated with the above arrangement is that the user will not receive any information why the session establishment request was accepted only partly, i.e. not as a whole, the reason being, for example, that the session already exists.